Many medical devices having a wide variety of clinical uses have been developed in recent years. For example, medical devices have been developed that can be used to replace indigenous mammalian organs that have become damaged and/or deteriorated, such as artificial heart valves or artificial joints; to help control or regulate defective organs, such as pacemakers; to replace damaged tissue, such as artificial skin grafts or breast implants; or to provide a less-invasive alternative to traditional treatment modalities, as is the case with intravascular therapeutic and diagnostic catheters. Such medical devices in the least often times represent a less traumatic treatment alternative, and often times, as is the case with artificial joints, represent the only viable treatment available.
However, such medical devices require exacting specifications in order to perform adequately under the rigorous conditions in which they are required to perform. Depending on the end use, such medical devices may be primarily comprised of polymeric materials that are non-thrombogenic, non-immunogenic, flexible, manipulatable, that exhibit both radial and longitudinal strength and/or, in certain applications, that are biodegradable. Inasmuch as there are very few single polymeric materials that provide this combination of characteristics, most medical devices are comprised of more than one polymeric material to provide the desired combination of physical properties. The use of multiple polymeric materials, in turn, requires that the polymeric materials be securely bonded together, as by the use of adhesive; direct bonding techniques, such as thermal bonding; and the like.
The bond sites of such medical devices, of course, are subject to the same exacting specifications of the overall device and thus, desirably exhibit a high degree of strength and integrity. For example, the bond sites must be able to withstand the handling and motion required to insert the device. Such bond sites also must be able to withstand the rigorous sterilization regimens, e.g., autoclave, ethylene oxide and gamma radiation sterilization regimens, to which medical devices are typically subjected. Additionally, the bond sites must be able to withstand any external pressure applied by the tissue into which it may be implanted or utilized. In medical devices such as intravascular catheters, the bond sites must be able to withstand the relatively high internal pressures, e.g., as high as 10 atmospheres to about 20 or more atmospheres, utilized to inflate the balloon portion of such catheters. Such high internal pressure not only affects the bond between the shaft portion of a catheter and the balloon, but also, since such high pressures can cause the shaft portion of the catheter to stretch and constrict, may affect other bonds present along the length of the catheter. As a result of these rigorous conditions, such bond sites must be strong enough to resist failure.
In the case of adhesive bonding, bond failure or weakness can result from a variety of circumstances. For example, the application of inadequate amounts of adhesive, as well as uneven application of adhesive, to a bond site can result in weakness or failure of the bond. Additionally, the use of an adhesive, as opposed to a direct bonding method, renders the bond site susceptible to failure as a result of the physical and mechanical properties of the adhesive itself. Finally, most adhesives rely on only the physical interaction, e.g., polar interactions or van der Waal's forces, between the adhesive and the surface to which the adhesive is applied for strength and integrity. Such a limited physical interaction provides inadequate bond strength for some applications.
Bond failure can also result from poor adhesion of the polymeric materials involved. For example, silicone rubber, while exhibiting many properties and characteristics otherwise desirable in the manufacture of medical devices, is difficult to adhere to any material, including itself. Thus, although silicone rubber has desirably low thrombogenicity, and is flexible and manipulatable, the incorporation of silicone and silicone-containing polymers into medical devices is problematic as such polymers generally do not adhere adequately with other materials typically used in medical device applications. Although functionalized monomers may be incorporated into a polymer to improve the adhesion of polymeric materials, such monomeric formulation modifications may fundamentally alter other desirable properties of the material.
Thus, it would be desirable to provide a method for improving the bondability of polymeric materials, particularly polymeric materials comprising silicone, that does not substantially alter the desirable properties of the polymeric material. It would further be desirable to provide medical devices incorporating such polymeric materials so that the bond sites of such devices would exhibit the desired integrity and strength.